Whereas no problems are usually experienced in transferring heat from a collector (or source) that is located below the sink (or storage facility) with the use of conventional convection heat transfer techniques, considerable difficulty is experienced in properly transferring heat in systems where the collector is located at a higher elevation than the sink. In solar energy collection systems, for example, the collector is of necessity positioned above the sink requiring the use of external power and control systems to transfer heat from the higher to the lower elevation.
The present invention relates to a system capable of transferring heat automatically from a heat source of relatively high temperature to a heat sink of lower temperature and at an elevation below that of its source without the necessity of using an external source of energy. Although the present invention is not limited in its application to solar energy collection systems, it is readily apparent that with the emphasis presently being placed on the utilization of solar energy as both primary and auxiliary sources of heat, the transfer system of the invention disclosed herein constitutes an advancement of considerable importance in the art. Moreover, and with particular reference to the solar application, it should be noted that with the present invention it is possible to automatically operate as a heat trap while minimizing the transfer of heat in the reverse direction should the heat source become colder then the sink, as would occur at night in a solar heating system.
The foregoing advantages are accomplished in the present invention with the use of an evaporator that is located near the heat source, which may comprise a solar heat collector panel, for example, and a condenser that is located at an elevation lower than that of the evaporator and which may function to heat hot water for storage, for example. The source heat is transferred to a volatile fluid that absorbs the heat with an increase in temperature and a change of state from liquid to vapor. The vapor that has been thus generated is conveyed by appropriate piping to the condenser wherein the fluid liberates its latent heat while changing from vapor to liquid phase. The so-condensed liquid then drains from the condenser to a trap which regulates the flow of liquid through a check valve and further piping to a transfer tank that is located above the evaporator. The fluid in the transfer tank is maintained at a lower temperature than that of the evaporator as a result of being insulated from the heat source. A dual level control system, which may be float operated, is employed in the transfer tank such that as the level of liquid in the tank rises above the upper control level the drain valve is opened permitting the transfer of the liquid into the evaporator. When the level of liquid within the tank drops below the lower control level the drain valve is closed, permitting the cycle to begin anew as the transfer tank begins to refill. The check valve functions to prevent liquid from draining back into the condenser during the aforementioned cycle. It should also be noted that the heat transfer system of the present invention is hermetically closed in such manner as to contain only the liquid and vapor of the volatile fluid. Air and extraneour gases are thereby excluded.